Recently, technology that superimposes an optical signal on illumination light (visible light) from an illumination apparatus by using light intensity modulation or the like has been known. Thus, it is possible to transmit information as well as to irradiate the illumination light from the illumination apparatus.
In optical communication (visible light communication) using the illumination light, a transmission range is limited to a range in which the illumination light reaches unlike normal wireless communication. Accordingly, there is an advantage that a communication range can be confirmed visually, or the transmission range can be limited to a limited space (area). As an application system using such an advantage, there is known a position information system in which identification information is transmitted as an optical signal from each of a plurality of illumination apparatuses provided in a facility, and the identification information is received by an optical signal receiver provided in a moving body, thereby specifying a position (current position) of the moving body. By this position information system, it is possible to specify the position of the moving body in an indoor space in which radio waves of Global Positioning System (GPS) are difficult to reach.
Since the optical signal receiver installed to the moving body is operated by a battery, there is a demand for a reduction in power consumption. Conventionally, various techniques for suppressing power consumption of the optical signal receiver have been proposed (see, e.g., Japanese Unexamined Patent Publication Application No. 2000-146690). In Japanese Unexamined Patent Publication Application No. 2000-146690, power consumption is reduced by intermittently performing power supply to a light receiving unit provided in the optical signal receiver.
However, in the technique disclosed in Japanese Unexamined Patent Publication Application No. 2000-146690 of merely intermittently performing the power supply, a reduction in power consumption is not sufficient. That is, even in a state (standby state) where the optical signal from an illumination apparatus is not received, the reception of the optical signal is monitored and accordingly power is consumed to some extent. Further, in a state where the optical signal is transmitted from the illumination apparatus and received by the optical signal receiver, power is supplied continuously even when the same information is transmitted repeatedly. Thus, power is consumed wastefully.